The invention generally relates to a flat box finisher for applying mud (or mastic or joint compound) over taped joints on walls and ceilings. Usually, paint or wallpaper is then applied over the finished mud. The flat box finisher has no external springs, but has at least one internal support bar which acts as a spring for applying pressure to a corresponding dry wall finishing handle affixed to the flat box finisher. The internal support bar is surrounded by the mud while the device is in use. As a result of having no external spring, the flat box finisher may be reduced in size for smaller jobs or difficult to reach areas of a room. The internal support bar may also eliminate problems with external springs, such as the spring wearing out or becoming damaged during use or storage.
Flat box finishers have been around for a long time. For example, U.S. Pat. No. 7,318,716 to Castagnetta discloses a tool for applying mastic to drywall, having a flexible trowelling bar for smoothing and shaping the applied mastic. The curvature of the trowelling bar is controlled by the rotation of a cam that is positioned on a rigid support and that is directly coupled to the trowelling bar through a link. Springs are positioned between the rigid support and the trowelling bar to maintain tension on the link during rotation of the cam. The springs exert pressure on the trowelling bar through plungers having rounded feet that maintain consistent contact with the trowelling bar as the curvature of the trowelling bar changes.
U.S. Pat. No. 6,146,039 to Pool discloses a mud box having a bottom surface with an outlet orifice, sides, a cover pivotally attached along one edge, and a handle attached to the cover for positioning the box on a surface and applying extruding pressure to the cover for ejecting material through the orifice. A spring assembly is attached to the box and connected to apply extruding pressure to the cover. A primary lock is coupled to the spring assembly and the box, the primary lock has a locked position in which the spring assembly is prevented from applying extruding pressure to the cover and an unlocked position in which the spring assembly applies extruding pressure to the cover. The primary lock is activated by a wheel assembly which moves it into the locked position when the box and wheel assembly are disengaged from a surface and which moves it into the unlocked position when the wheel assembly and box are engaged with a surface.
U.S. Pat. No. 5,143,264 to MacMillan discloses a flat finishing box having attachable/detachable heads each of which have a structural part incorporating a mouth and to which an edge assembly and edge assembly adjustment apparatus are attached. Heads are provided for dispensing mud in each of the three standard swath widths, 7″, 10″ and 12″, so that any swath width can be dispensed from one box by interchanging heads attached to the box. The box cover is one extrusion and the bottom and back are another. The hinged edge of the cover has a cylindrical segment along the edge which fits into a partial cylindrical groove in the back, providing a leak proof hinge. Channels are provided to enhance mud flow from portions of the box beyond the width of the mouth of the head being used to the portion within the mouth width.
However, these existing flat box finishers fail to provide an internal support bar which acts as a spring and allows the top surface area of the flat box finisher to be reduced while still accommodating the surface area of the handle connector portion. Further, these existing flat box finishers fail to provide an internal support bar which acts as a spring therein making the device cost effective and efficient. A need, therefore, exists for an improved flat box finisher which allows a user to easily, cheaply and conveniently apply mud to a limited area around tape while preparing drywall.